Mixer amplifier



Feb. 13, 1934,

H. C. BAUMANN MIXER AMPLIFIER Filed April 4, 1931 A TT() N15 y Patented Feb. 13, 1934 MIXER ANIPLIFIER Harold can Baumann, Elizabeth, N. J., assignmto United Research Corporation, New York, N. Y., a corporation of Delaware Application April 4, 1931. Serial No. 527,674

Claims.

The invention relates to mixer amplifiers wherein use is made of a plurality of pick-up devices, such as microphones, phonograph pickups, or other sources of electrical wave energy,

'.5 andwherein the output therefrom is amplified and led to a common output circuit.

This arrangement requires that a potentiometer or the like be employed so that the relative intensity of the energy in each of the pickup circuits may be controlled or adjusted to proper intensity.

An object of the present invention is to regulate the current in each of the pick-up or input circuits without thereby alfecting the intensity of the current in the other input circuits.

Another object is to regulate the current in the common or output circuit without thereby alectng the intensity of the currents in the input circuits.

A further object is to make the impedances of the input circuits and of the common circuit independent of each other.

Still another object is to make the impedance of the common circuit independent of the number of input circuits operatively associated with the common circuit.

` These objects are accomplished by taking advantage of the unilateral conducting property of an ordinary audion amplier or other electron `discharge device which is employed to isolate each input circuit from the effects of the potentiometers or the like in the other circuits and which may also amplify the current in each input circuit.

For further details of the invention, reference may be made to the accompanying drawing, wherein:

Figs. 1 and 2 illustrate alternative circuit arrangements which may be employed.

Referring to Fig. 1, there are employed a plurality of input circuits 1, 2, 3, 4, connected individually to the input circuits of vacuum tube amplifiers 5, 6, 7 and 8, respectively. The output circuits of the ampliers 5 to 8, inclusive, are connected in parallel and feed into a common output circuit 9.

' The input circuit 1 comprises a microphone pick-up 10 in circuit with a polarizing battery 11, ampliiier 12, and the primary winding of a transformer 13. Across the secondary winding of the transformer 13 is connected a potentiometer 14 in circuit with a transformer 15, the secondary winding of which is connected in the input circuit of amplifier 5.

The other input circuits 2, 3 and 4 are similarly connected to their respective ampliers 6, 7 and 8 with this difference: Instead of the microphone 10 as a pick-up device, use may be made in one or more or all of the input circuits of phonograph pick-ups, such as 10a. Alternatively, some of the pick-up devices may be phonograph pick-ups.'

circuits not in use may be short circuited by switches or plugs, such as 41.

Transformers 13 and 15, and the-corresponding transformers in the other input circuits, substantially match theimpedances inrtheir respective input and output circuits, as is well known in the art.

The common output circuit 9, which may lead;

for example, to a recording device for wax or iilm recording, or both, or to a reproducer or the like, comprises a transformer 16, in the secondary circuit of which is provided a master potentiometer 17 for controlling the intensity of thev combined current to the recording or other device.

On referring to Fig. 1, it will be seen that the use of the amplifiers 5, 6, 7 and 8 individual to the input circuits will prevent the adjustment of potentiometer 14,101* the corresponding potentiometers in the other input circuits, or the operation of switches, such as 41, from effecting the impedance of the remaining input circuits; and these ampliers will also prevent the adjustment of the master potentiometer 17 from affecting the impedance of the individual input circuits.

The above noted advantages are also present in the circuit of Fig. 2, wherein the input circuits 18, 19, 20, 21, 22, 23, each comprising a potentiometer, such as 24, transformer 25, and input circuit of vacuum tube amplier 26, work into a common output circuit 27 comprising a parallel connection of the plate circuits of the ampliers, such as 26.

The common output circuit 27 comprises a transformer 28, the secondary winding 29 of which is in circuit with a master potentiometer 30 connected in an output circuit 31, which leads to the lm or wax recorder, reproducer, or the like.

The lamentary cathodes, such as 32, of al1 lio of the amplifiers, such as 26, in Fig. 2, are connected in series with a suitable source, as indicated. A master resistance for all of the iilaments is illustrated at 33. The grid bias for each of the vacuum tubes, such as 26, is obtained by a connection through a resistance, such as 36, to a more` negative point in the filament circuit.-

Resistances 34and 35: are connected in. series with.

the cathodes to provide grid bias for vacuum tubes 26a. and 26h in Fig. 2. Resistances 36 and the like are connected in series with the secondarywindings of transformers, such as 25, andare of the order of 50,000 ohms, their purpose being, in cooperation with bypass condensers, suchas 37, to prevent or reduce cross talk between the input circuits and to reduce disturbances which.

may be picked up by the connections to the lament supply.

In order to suppress any iiuctuations that may exist in the plate supply of the amplifiers, such as 26, there is employeda' lter comprising a re sistance 38, ofabout 10,000 ohms, shunted by two-condensers- 39-and 40, the mid-point offtheser condenser-s being connected to ground, and this lter as a wholebeing inseries with the plate circuit;

Theimpedances, voltages and capacities indicated in the drawings havebeen found to give good results in-practice. It should be understood, however, that the invention is-not dependent upon the particular values off the impedances, voltages or' capacities shown therein.

The embodiments of the invention illustrated and described herein have been selected for the purpose of clearlyV setting forth the principles involved. Further embodiments may be made, however, without departurefrom the inventive conceptdisclosed, and it is intended that the invention be limited only by the spirit and scope of the appended claims.

I claim-t 1. In combination, a plurality of individual lines each comprisinga source off audio frequencyenergy, a potentiometer connected across the line', an impedance-matching transformer inserted in the line between the source and the potentiometer, an electron tube having a gridcircuit andan anode circuit connected therewith, and a second impedance-matchingtransformer inserted in the line intermediate the potentiometer andthe-grid circuit of said tube and having its primary winding connected toa variable tap on said potentiometer; an output transformer, a master potentiometer connected across the secondary winding of said output transformer, a connection common to the plate circuits of the electron tubes in said individualv lines and the primary winding ofv said output transformer, and an output circuit connected to a variable tap on said master potentiometer whereby the level off audio frequency energy from any of said sources may be changed independently and the level of the combined audio frequency energy in said output circuit may be changed without af- .I fecting the relative levels of the audio frequency energy inthe individual lines.

2, The combination of a plurality of vacuum tube devices each having a grid, a cathode and a plate, an in-put circuit connected to each of said grids, a grounded source of potential connected to said cathodes in series, circuits for said plates, one of said in-put circuits comprisingA a connection from4 the grid.V of one ofY said tubes to the cathode of another of said tubes, said connection comprising a high resistance, and a condenser path to ground for said high resistance.

3. The combination of a plurality of vacuum tube devices each having a grid, a cathode and a plate, an in-put circuit connected to each of said grids, a grounded source of potential connected to said cathodes in series, circuits for said plates, one of said: in-putv circuits comprising a connection from the grid'- of one of said tubes to the cathode of another of said tubes, and means for preventing or reducing interference which would otherwise occur between said in-put circuits due to said connection.

4'. The combination of a plurality of vacuum tube devices' each` having a grid, a cathode and a plate, an in-put circuit for each of said grids, aV common out-put circuit for said plates, said cathodes being. connected in series and a grounded source ofl potential therefor, a plurality of paths each.- including a high resistance, and a condenser connected at one terminal to ground and at the other terminal to various points along` said cathode circuit, and connections between each*v off ai' plurality of said grids and a particular one, of said high-.resistances respectively.

5. The combination of a pluralityof vacuum. tube devices each having a. grid, a cathode-.anda` plate, an. in-put circuiti connectedto eachofl said grids, a common out-put' circuit, saidlplates being connected in parallel and to said out-put circut',A said cathodes being connected in seriesv and a: grounded source of potential therefor, connections between each of said grids` and the cathode of a succeeding tube respectively, said last.- mentioned connections each including a high; resistance one terminal of which leadsA to the; cathode. circuit and the other` terminal of.' which leadsithrougha condenser to ground.

6. A mixer circuit comprising a plurality.: of'

vindividual lines, each comprising a source` of' audio frequency energy, a potentiometerw connectedi across the line, a vacuum tube hav-ing: a grid, a cathode and a plate foreach line, atransformer in each line between the potentiometer andi its associatedz vacuum tube, a common out.- put circuit', means'. for connecting said' plates in parallel and to said out-put circuit', a circuit for connecting said cathodes in series, a grounded source of potentialA` for said cathode circuit, a. secondary winding ofv each of' said transformers being in circuit with the grid of one of said tubes. and.' with the cathode of another of said' tubes, a. high resistance of the order of several thousand ohms in each4 of said last-mentioned circuits. and. connected between the secondary windingr forone tube and the cathode of another tube, and a path to ground including a condenser con.- nected between each of said high resistancesand its associatedY secondary winding whereby interference between associated in-put circuits isA re'- duced.

7'. A mixer circuit comprising a plurality of in-put circuits each having a vacuum tube ampliiier; each ampliiier having an in-put circuit and an out-put circuit, each of said ampliiiers, having a grid, a cathode and a plate, circuits for said plates, and a connection from the grid of each of said tubes to the cathode of another tube comprising means for reducing' interference between associated in-put circuits.

8. The combination of a plurality of vacuum tube devices each having a grid, a cathode andv a plate, an in-put circuit connected to cach of: said grids, a grounded source of potential'. connected to said cathodes in series, circuits for said plates, a high resistance. connected between. the

lill

grid of one of said tubes and the cathode of another of said tubes, and a condenser connected between the grid terminal of said high resistance and a point in said series cathode circuit.

9. The combination of a plurality of vacuum tube devices each having a grid, a cathode `and a plate, an in-put circuit connected to each of said grids, a grounded source of potential connected to said cathodes in series, circuits for said plates, one of said in-put circuits comprising a grid biasing high resistance in shunt between the grid terminal of said high resistance and the cathode of the tube for which said high resistance serves as a grid bias.

10. The combination of a plurality of vacuum tube devices each having a grid, a cathode and a plate, an in-put circuit connected to each of said grids, a common out-put circuit, said plates being connected in parallel and to said out-put circuit, said cathodes being connected in series and a grounded source of potential therefor, grid biasing connections comprising a high resistance between each of said grids and the cathode of a succeeding tube respectively, and a condenser path for each of said high resistances and connected in shunt to the grid terminal of its repective high resistance at one terminal, and at the other terminal to the cathode of the tube for which the respective high resistance serves as a grid bias.

HAROLD CARL BAUMANN. 

